The present invention relates to a hydraulically-actuated starting clutch, and more specifically to a starting clutch assembly for a continuously variable transmission in an automotive vehicle. Continuously variable transmissions have been known for several years as a driving assembly between a vehicle engine and the road engaging wheels to provide smooth acceleration without the usual gear shifting found in most automatic transmissions. A continuously variable transmission includes a pair of variable sheave pulleys, an endless belt extending between and engaging the pulleys, and control means to alter the effective pulley diameters and thus change the belt ratio.
In automotive applications, it is necessary to incorporate a suitable clutch assembly in the drivetrain as a starting device and planetary gearing to effect desirable gear reduction and to provide for forward-neutral-reverse gear mechanisms. It is desirable to have the pulleys constantly rotating when the vehicle engine is running, even at idle rpm, so that initiation of vehicle movement is accomplished by a speed responsive friction starting device, such as a clutch, located at the output of the continuously variable transmission, and a forward-neutral-reverse mechanism is desirably located in conjunction with or subsequent to the starting device.
In a starting clutch where actuation is dependent upon hydraulic pressure acting on the clutch engaging elements and where circulating oil is utilized for cooling of the friction faces, the viscous drag resulting from the oil flowing between the clutch surfaces when the clutch is in its released state results in a condition where the clutch is not fully disengaged. Therefore, unwanted driving input to the transmission is present after release of the clutch. The undesirable vehicle "creep" that results often requires the use of a special brake in the system; an inefficient and costly extra. A possible solution to this problem is the strategic dumping of the cooling oil flowing to the clutch together with the clutch's ability to promptly respond.
Another problem resides in the resultant centrifugal force of hydraulic actuating fluid for a rotating clutch which provides liquid pressure that may influence actuation of the clutch piston in its chamber. Further problems include engine stalling during rapid vehicle braking and lack of smoothness of clutch engagement during acceleration of the vehicle. The present invention overcomes these various problems in the form of a novel simplified hydraulically-actuated starting clutch assembly.